The Thinking
Machine—Professor Augustus S. F. X.
Van Dusen, Ph. D, LL. D., F. R. S., M. D., etc., scientist and
logician—listened intently and without comment to a weird, seemingly
inexplicable story. Hutchinson Hatch, reporter, was telling it. The bowed
figure of the savant lay at ease in a large chair. The enormous head with its
bushy yellow hair was thrown back, the thin, white fingers were pressed tip to
tip and the blue eyes, narrowed to mere slits, squinted aggressively upward.
The scientist was in a receptive mood.

“From
the beginning, every fact you know,” he had requested.

“It’s all out
in the Back Bay,” the reporter explained. “There is a big apartment house
there, a fashionable establishment, in a side street, just off Commonwealth
Avenue. It is five stories in all, and is cut up into small suites, of two and
three rooms with a bath. These suites are handsomely, even luxuriously
furnished, and are occupied by people who can afford to pay big rents.
Generally these are young unmarried men, although in several cases they are
husband and wife. It is a house of every modern improvement, elevator service,
hall boys, liveried door men, spacious corridors and all that. It has both the
gas and electric systems of lighting. Tenants are at liberty to use either or
both.

“A young
broker, Weldon Henley, occupies one of the handsomest of these suites, being on
the second floor, in front. He has met with considerable success in the Street.
He is a bachelor and lives there alone. There is no personal servant. He
dabbles in photography as a hobby, and is said to be remarkably expert.

“Recently
there was a report that he was to be married this Winter to a beautiful
Virginia girl who has been visiting Boston from time to time, a Miss
Lipscomb—Charlotte Lipscomb, of Richmond. Henley has never denied or affirmed
this rumor, although he has been asked about it often. Miss Lipscomb is
impossible of access even when she visits Boston. Now she is in Virginia, I
understand, but will return to Boston later in the season.”

The reporter
paused, lighted a cigarette and leaned forward in his chair, gazing steadily
into the inscrutable eyes of the scientist.

“When Henley
took the suite he requested that all the electric lighting apparatus be removed
from his apartments,” he went on. “He had taken a long lease of the place, and
this was done. Therefore he uses only gas for lighting purposes, and he usually
keeps one of his gas jets burning low all night.”

“Bad, bad for
his health,” commented the scientist.

“Now comes the
mystery of the affair,” the reporter went on. “It was five weeks or so ago
Henley retired as usual—about midnight. He locked his door on the inside—he is
positive of that—and awoke about four o’clock in the morning nearly asphyxiated
by gas. He was barely able to get up and open the window to let in the fresh
air. The gas jet he had left burning was out, and the suite was full of gas.”

“Accident,
possibly,” said The Thinking Machine. “A draught through the apartments; a
slight diminution of gas pressure; a hundred possibilities.”

“So it was
presumed,” said the reporter. “Of course it would have been impossible for——”

“Well, then,
it seems highly improbable that the door had been opened or that anyone came
into the room and did this deliberately,” the newspaper man went on, with a
slight smile. “So Henley said nothing about this; attributed it to accident.
The next night he lighted his gas as usual, but he left it burning a little
brighter. The same thing happened again.”

“Ah,” and The
Thinking Machine changed his position a little. “The second time.”

“And again he
awoke just in time to save himself,” said Hatch. “Still he attributed the
affair to accident, and determined to avoid a recurrence of the affair by doing
away with the gas at night. Then he got a small night lamp and used this for a
week or more.”

“Why does he
have a light at all?” asked the scientist, testily.

“I can hardly
answer that,” replied Hatch. “I may say, however, that he is of a very nervous
temperament, and gets up frequently during the night. He reads occasionally
when he can’t sleep. In addition to that he has slept with a light going all
his life; it’s a habit.”

“Go on.”

“One night he
looked for the night lamp, but it had disappeared—at least he couldn’t find
it—so he lighted the gas again. The fact of the gas having twice before gone
out had been dismissed as a serious possibility. Next morning at five o’clock a
bell boy, passing through the hall, smelled gas and made a quick investigation.
He decided it came from Henley’s place, and rapped on the door. There was no
answer. It ultimately developed that it was necessary to smash in the door.
There on the bed they found Henley unconscious with the gas pouring into the
room from the jet which he had left lighted. He was revived in the air, but for
several hours was deathly sick.”

“Why was the
door smashed in?” asked The Thinking Machine. “Why not unlocked?”

“It was done
because Henley had firmly barred it,” Hatch explained. “He had become
suspicious, I suppose, and after the second time he always barred his door and
fastened every window before he went to sleep. There may have been a fear that
some one used a key to enter.”

“Well?” asked
the scientist. “After that?”

“Three weeks
or so elapsed, bringing the affair down to this morning,” Hatch went on. “Then
the same thing happened a little differently. For instance, after the third
time the gas went out Henley decided to find out for himself what caused it,
and so expressed himself to a few friends who knew of the mystery. Then, night
after night, he lighted the gas as usual and kept watch. It was never disturbed
during all that time, burning steadily all night. What sleep he got was in daytime.

“Last night
Henley lay awake for a time; then, exhausted and tired, fell asleep. This
morning early he awoke; the room was filled with gas again. In some way my city
editor heard of it and asked me to look into the mystery.”

That was all.
The two men were silent for a long time, and finally The Thinking Machine
turned to the reporter.

“Does anyone
else in the house keep gas going all night?” he asked.

“I don’t
know,” was the reply. “Most of them, I know, use electricity.”

“Nobody else
has been overcome as he has been?”

“No. Plumbers
have minutely examined the lighting system all over the house and found nothing
wrong.”

“Does the gas
in the house all come through the same meter?”

“Yes, so the
manager told me. I supposed it possible that some one shut it off there on
these nights long enough to extinguish the lights all over the house, then
turned it on again. That is, presuming that it was done purposely. Do you think
it was an attempt to kill Henley?”

“It might be,”
was the reply. “Find out for me just who in the house uses gas; also if anyone
else leaves a light burning all night; also what opportunity anyone would have
to get at the meter, and then something about Henley’s love affair with Miss
Lipscomb. Is there anyone else? If so, who? Where does he live? When you find
out these things come back here.”

••••••

That afternoon
at one o’clock Hatch returned to the apartments of The Thinking Machine, with
excitement plainly apparent on his face.

“Well?” asked
the scientist.

“A French
girl, Louise Regnier, employed as a maid by Mrs. Standing in the house, was
found dead in her room on the third floor to-day at noon,” Hatch explained
quickly. “It looks like suicide.”

“How?” asked
The Thinking Machine.

“The people
who employed her—husband and wife—have been away for a couple of days,” Hatch
rushed on. “She was in the suite alone. This noon she had not appeared, there
was an odor of gas and the door was broken in. Then she was found dead.”

“With the gas
turned on?”

“With the gas
turned on. She was asphyxiated.”

“Dear me, dear
me,” exclaimed the scientist. He arose and took up his hat. “Let’s go and see
what this is all about.”

II

When Professor Van Dusen and Hatch
arrived at the apartment house they had been preceded by the Medical Examiner
and the police. Detective Mallory, whom both knew, was moving about in the
apartment where the girl had been found dead. The body had been removed and a
telegram sent to her employers in New York.

“Too late,”
said Mallory, as they entered.

“What was it,
Mr. Mallory?” asked the scientist.

“Suicide,” was
the reply. “No question of it. It happened in this room,” and he led the way
into the third room of the suite. “The maid, Miss Regnier, occupied this, and
was here alone last night. Mr. and Mrs. Standing, her employers, have gone to
New York for a few days. She was left alone, and killed herself.”

Without
further questioning The Thinking Machine went over to the bed, from which the
girl’s body had been taken, and, stooping beside it, picked up a book. It was a
novel by “The Duchess.” He examined this critically, then, standing on a chair,
he examined the gas jet. This done, he stepped down and went to the window of
the little room. Finally The Thinking Machine turned to the detective.

“Just how much
was the gas turned on?” he asked.

“Turned on
full,” was the reply.

“Were both the
doors of the room locked?”

“Both, yes.”

“Any cotton,
or cloth, or anything of the sort stuffed in the cracks of the window?”

“No. It’s a
tight-fitting window, anyway. Are you trying to make a mystery out of this?”

“Cracks in the
doors stuffed?” The Thinking Machine went on.

“No.” There
was a smile about the detective’s lips.

The Thinking
Machine, on his knees, examined the bottom of one of the doors, that which led
into the hall. The lock of this door had been broken when employees burst into
the room. Having satisfied himself here and at the bottom of the other door,
which connected with the bedroom adjoining, The Thinking Machine again climbed
on a chair and examined the doors at the top.

“Both transoms
closed, I suppose?” he asked.

“Yes,” was the
reply. “You can’t make anything but suicide out of it,” explained the
detective. “The Medical Examiner has given that as his opinion—and everything I
find indicates it.”

After awhile
Detective Mallory went away. Hatch and the scientist went down to the office
floor, where they saw the manager. He seemed to be greatly distressed, but was
willing to do anything he could in the matter.

“Perfectly,”
was the reply. “One of the best and most reliable men I ever met. Alert and
wide-awake.”

“Can I see him
a moment? The night man, I mean?”

“Certainly,”
was the reply. “He’s downstairs. He sleeps there. He’s probably up by this
time. He sleeps usually till one o’clock in the daytime, being up all night.”

“Do you supply
gas for your tenants?”

“Both gas and
electricity are included in the rent of the suites. Tenants may use one or
both.”

“And the gas
all comes through one meter?”

“Yes, one
meter. It’s just off the engine room.”

“I suppose
there’s no way of telling just who in the house uses gas?”

“No. Some do
and some don’t. I don’t know.”

This was what
Hatch had told the scientist. Now together they went to the basement, and there
met the night engineer, Charles Burlingame, a tall, powerful, clean-cut man, of
alert manner and positive speech. He gazed with a little amusement at the
slender, almost childish figure of The Thinking Machine and the grotesquely
large head.

“You are in
the engine room or near it all night every night?” began The Thinking Machine.

“I haven’t
missed a night in four years,” was the reply.

“Anybody ever
come here to see you at night?”

“Never. It’s
against the rules.”

“The manager
or a hall boy?”

“Never.”

“In the last
two months?” The Thinking Machine persisted.

“Not in the
last two years,” was the positive reply. “I go on duty every night at seven
o’clock, and I am on duty until seven in the morning. I don’t believe I’ve seen
anybody in the basement here with me between those hours for a year at least.”

The Thinking
Machine was squinting steadily into the eyes of the engineer, and for a time
both were silent. Hatch moved about the scrupulously clean engine room and
nodded to the day engineer, who sat leaning back against the wall. Directly in
front of him was the steam gauge.

“Have you a
fireman?” was The Thinking Machine’s next question.

“No. I fire
myself,” said the night man. “Here’s the coal,” and he indicated a bin within
half a dozen feet of the mouth of the boiler.

“I don’t
suppose you ever had occasion to handle the gas meter?” insisted The Thinking
Machine.

“Never touched
it in my life,” said the other. “I don’t know anything about meters, anyway.”

“And you never
drop off to sleep at night for a few minutes when you get lonely? Doze, I
mean?”

The engineer
grinned good-naturedly.

“Never had any
desire to, and besides I wouldn’t have the chance,” he explained. “There’s a
time check here,”—and he indicated it. “I have to punch that every half hour
all night to prove that I have been awake.”

“Dear me, dear
me,” exclaimed The Thinking Machine, irritably. He went over and examined the
time check—a revolving paper disk with hours marked on it, made to move by the
action of a clock, the face of which showed in the middle.

“Besides
there’s the steam gauge to watch,” went on the engineer. “No engineer would
dare go to sleep. There might be an explosion.”

“Do you know
Mr. Weldon Henley?” suddenly asked The Thinking Machine.

“Who?” asked
Burlingame.

“Weldon
Henley?”

“No-o,” was
the slow response. “Never heard of him. Who is he?”

“One of the
tenants, on the second floor, I think.”

“Lord, I don’t
know any of the tenants. What about him?”

“When does the
inspector come here to read the meter?”

“I never saw
him. I presume in daytime, eh Bill?” and he turned to the day engineer.

“Always in the
daytime—usually about noon,” said Bill from his corner.

“Any other
entrance to the basement except this way—and you could see anyone coming here
this way I suppose?”

“Sure I could
see ’em. There’s no other entrance to the cellar except the coal hole in the
sidewalk in front.”

“Two big
electric lights in front of the building, aren’t there?”

“Yes. They go
all night.”

A slightly
puzzled expression crept into the eyes of The Thinking Machine. Hatch knew from
the persistency of the questions that he was not satisfied; yet he was not able
to fathom or to understand all the queries. In some way they had to do with the
possibility of some one having access to the meter.

“Where do you
usually sit at night here?” was the next question.

“Over there
where Bill’s sitting. I always sit there.”

The Thinking
Machine crossed the room to Bill, a typical, grimy-handed man of his class.

“May I sit
there a moment?” he asked.

Bill arose
lazily, and The Thinking Machine sank down into the chair. From this point he
could see plainly through the opening into the basement proper—there was no
door—the gas meter of enormous proportions through which all the gas in the
house passed. An electric light in the door made it bright as daylight. The
Thinking Machine noted these things, arose, nodded his thanks to the two men and,
still with the puzzled expression on his face, led the way upstairs. There the
manager was still in his office.

“I presume you
examine and know that the time check in the engineer’s room is properly punched
every half-hour during the night?” he asked.

“Yes. I
examine the dial every day—have them here, in fact, each with the date on it.”

“May I see
them?”

Now the
manager was puzzled. He produced the cards, one for each day, and for half an
hour The Thinking Machine studied them minutely. At the end of that time, when
he arose and Hatch looked at him inquiringly, he saw still the perplexed
expression.

After urgent
solicitation, the manager admitted them to the apartments of Weldon Henley. Mr.
Henley himself had gone to his office in State Street. Here The Thinking
Machine did several things which aroused the curiosity of the manager, one of
which was to minutely study the gas jets. Then The Thinking Machine opened one
of the front windows and glanced out into the street. Below fifteen feet was
the sidewalk; above was the solid front of the building, broken only by a
flagpole which, properly roped, extended from the hall window of the next floor
above out over the sidewalk a distance of twelve feet or so.

“Ever use that
flagpole?” he asked the manager.

“Rarely,” said
the manager. “On holidays sometimes—Fourth of July and such times. We have a
big flag for it.”

From the
apartments The Thinking Machine led the way to the hall, up the stairs and to
the flagpole. Leaning out of this window, he looked down toward the window of
the apartments he had just left. Then he inspected the rope of the flagpole,
drawing it through his slender hands slowly and carefully. At last he picked
off a slender thread of scarlet and examined it.

“Ah,” he
exclaimed. Then to Hatch: “Let’s go, Mr. Hatch. Thank you,” this last to the
manager, who had been a puzzled witness.

Once on the
street, side by side with The Thinking Machine, Hatch was bursting with
questions, but he didn’t ask them. He knew it would be useless. At last The
Thinking Machine broke the silence.

“That girl,
Miss Regnier, was murdered,” he said
suddenly, positively. “There have been four attempts to murder Henley.”

“How?” asked
Hatch, startled.

“By a scheme
so simple that neither you nor I nor the police have ever heard of it being
employed,” was the astonishing reply. “It
is perfectly horrible in its simplicity.”

“What was it?”
Hatch insisted, eagerly.

“It would be
futile to discuss that now,” was the rejoinder. “There has been murder. We know
how. Now the question is—who? What person would have a motive to kill Henley?”

III

There was a pause as they walked on.

“Where are we
going?” asked Hatch finally.

“Come up to my
place and let’s consider this matter a bit further,” replied The Thinking
Machine.

Not another
word was spoken by either until half an hour later, in the small laboratory.
For a long time the scientist was thoughtful—deeply thoughtful. Once he took
down a volume from a shelf and Hatch glanced at the title. It was “Gases: Their
Properties.” After awhile he returned this to the shelf and took down another,
on which the reporter caught the title, “Anatomy.”

“Now, Mr.
Hatch,” said The Thinking Machine in his perpetually crabbed voice, “we have a
most remarkable riddle. It gains this remarkable aspect from its very
simplicity. It is not, however, necessary to go into that now. I will make it
clear to you when we know the motives.

“As a general
rule, the greatest crimes never come to light because the greatest criminals,
their perpetrators, are too clever to be caught. Here we have what I might call
a great crime committed with a subtle simplicity that is wholly disarming, and
a greater crime even than this was planned. This was to murder Weldon Henley.
The first thing for you to do is to see Mr. Henley and warn him of his danger.
Asphyxiation will not be attempted again, but there is the possibility of
poison, a pistol shot, a knife, anything almost. As a matter of fact, he is in
great peril.

“Superficially,
the death of Miss Regnier, the maid, looks to be suicide. Instead it is the
fruition of a plan which has been tried time and again against Henley. There is
a possibility that Miss Regnier was not an intentional victim of the plot, but
the fact remains that she was murdered. Why? Find the motive for the plot to
murder Mr. Henley and you will know why.”

The Thinking
Machine reached over to the shelf, took a book, looked at it a moment, then
went on:

“The first
question to determine positively is: Who hated Weldon Henley sufficiently to
desire his death? You say he is a successful man in the Street. Therefore there
is a possibility that some enemy there is at the bottom of the affair, yet it
seems hardly probable. If by his operations Mr. Henley ever happened to wreck
another man’s fortune find this man and find out all about him. He may be the
man. There will be innumerable questions arising from this line of inquiry to a
man of your resources. Leave none of them unanswered.

“On the other
hand there is Henley’s love affair. Had he a rival who might desire his death?
Had he any rival? If so, find out all about him. He may be the man who planned
all this. Here, too, there will be questions arising which demand answers.
Answer then—all of them—fully and clearly before you see me again.

“Was Henley
ever a party to a liason of any kind? Find that out, too. A vengeful woman or a
discarded sweetheart of a vengeful woman, you know, will go to any extreme. The
rumor of his engagement to Miss—Miss——”

“Miss
Lipscomb,” Hatch supplied.

“The rumor of
his engagement to Miss Lipscomb might have caused a woman whom he had once been
interested in or who was once interested in him to attempt his life. The
subtler murders—that is, the ones which are most attractive as problems—are
nearly always the work of a cunning woman. I know nothing about women myself,”
he hastened to explain; “But Lombroso has taken that attitude. Therefore, see
if there is a woman.”

Most of these
points Hatch had previously seen—seen with the unerring eye of a clever
newspaper reporter—yet there were several which had not occurred to him. He
nodded his understanding.

“Now the
center of the affair, of course,” The Thinking Machine continued, “is the
apartment house where Henley lives. The person who attempted his life either
lives there of has ready access to the place, and frequently spends the night
there. This is a vital question for you to answer. I am leaving all this to you
because you know better how to do these things than I do. That’s all, I think.
When these things are all learned come back to me.”

The Thinking
Machine arose as if the interview were at an end, and Hatch also arose,
reluctantly. An idea was beginning to dawn in his mind.

“Does there
occur to you that there is any connection whatever between Henley and Miss
Regnier?” he asked.

“It is
possible,” was the reply. “I had thought of that. If there is a connection it
is not apparent yet.”

“Then how—how
was it she—she was killed, or killed herself, whichever may be true, and——”

“The attempt
to kill Henley killed her. That’s all I can say now.”

“That all?”
asked Hatch, after a pause.

“No. Warn Mr.
Henley immediately that he is in grave danger. Remember the person who has
planned this will probably go to any extreme. I don’t know Mr. Henley, of
course, but from the fact that he always had a light at night I gather that he
is a timid sort of man—not necessarily a coward, but a man lacking in
stamina—therefore, one who might better disappear for a week or so until the
mystery is cleared up. Above all, impress upon him the importance of the
warning.”

The Thinking
Machine opened his pocketbook and took from it the scarlet thread which he had
picked from the rope of the flagpole.

“Here, I
believe, is the real clew to the problem,” he explained to Hatch. “What does it
seem to be?”

Hatch examined
it closely.

“I should say
a strand from a Turkish bath robe,” was his final judgement.

“Possibly. Ask
some cloth expert what he makes of it, then if it sounds promising look into
it. Find out if by any possibility it can be any part of any garment worn by
any person in the apartment house.”

“But it’s so
slight——” Hatch began.

“I know,” the
other interrupted, tartly. “It’s slight, but I believe it is a part of the
wearing apparel of the person, man or woman, who has four times attempted to
kill Mr. Henley and who did kill the girl. Therefore, it is important.”

Hatch looked
at him quickly.

“Well, how—in
what manner—did it come where you found it?”

“Simple
enough,” said the scientist. “It is a wonder that there were not more pieces of
it—that’s all.”

Perplexed by
his instructions. But confident of results, Hatch left The Thinking Machine.
What possible connection could this tiny bit of scarlet thread, found on a
flagpole, have with one shutting off the gas in Henley’s rooms? How did anyone
go into Henley’s rooms to shut off the gas? How was it Miss Regnier was dead?
What was the manner of her death?

A cloth expert
in a great department store turned his knowledge on the tiny bit of scarlet for
the illumination of Hatch, but he could go no further than to say that it
seemed to be part of a Turkish bath robe.

“Man or
woman’s?” asked Hatch.

“The material
from which bath robes are made is the same for both men and women,” was the
reply. “I can say nothing else. Of course there’s not enough of it to even
guess at the pattern of the robe.”

Then Hatch
went to the financial district and was ushered into the office of Weldon
Henley, a slender, handsome man of thirty-two or three years, pallid of face
and nervous in manner. He still showed the effect of the gas poisoning, and
there was even a trace of a furtive fear—fear of something, he himself didn’t
know what—in his actions.

Henley talked
freely to the newspaper man of certain things, but of other things he was
resentfully reticent. He admitted his engagement to Miss Lipscomb, and finally
even admitted that Miss Lipscomb’s hand had been sought by another man,
Regnault Cabell, formerly of Virginia.

“Could you
give me his address?” asked Hatch.

“He lives in
the same apartment house with me—two floors above,” was the reply.

Hatch was
startled; startled more than he would have cared to admit.

“Are you on
friendly terms with him?” he asked.

“Certainly,”
said Henley. “I won’t say anything further about this matter. It would be
unwise for obvious reasons.”

“I suppose you
consider that this turning on of the gas was an attempt on your life?”

“I can’t
suppose anything else.”

Hatch studied
the pallid face closely as he asked the next question.

“Do you know
Miss Regnier was found dead to-day?”

“Dead?”
exclaimed the other, and he arose. “Who—what—who is she?”

It seemed a
distinct effort for him to regain control of himself.

The reporter
detailed then the circumstances of the finding of the girl’s body, and the
broker listened without comment. From that time forward all the reporter’s
questions were either parried or else met with a flat refusal to answer.
Finally Hatch repeated to him the warning which he had from The Thinking
Machine, and feeling that he had accomplished little, went away.

At eight
o’clock that night—a night of complete darkness—Henley was found unconscious,
lying in a little used walk in the Common. There was a bullet hole through his
left shoulder, and he was bleeding profusely. He was removed to the hospital,
where he regained consciousness for just a moment.

“Who shot
you?” he was asked.

“None of your
business,” he replied, and lapsed into unconsciousness.

IV

Entirely unaware of this latest attempt
on the life of the broker, Hutchinson Hatch steadily pursued his investigations.
They finally led him to an intimate friend of Regnault Cabell. The young
Southerner had apartments on the fourth floor of the big house off Commonwealth
Avenue, directly over those Henley occupied, but two flights higher up. This
friend was a figure in the social set of the Back Bay. He talked to Hatch
freely of Cabell.

“He’s a good
fellow,” he explained, “one of the best I ever met, and comes of one of the
best families Virginia ever had—a true F. F. V. He’s pretty quick tempered and
all that, but an excellent chap, and everywhere he has gone here he has made
friends.”

“He used to be
in love with Miss Lipscomb of Virginia, didn’t he?” asked Hatch, casually.

“Used to be?”
the other repeated with a laugh. “He is
in love with her. But recently he understood that she was engaged to Weldon
Henley, a broker—you may have heard of him?—and that, I suppose, has dampened
his ardor considerably. As a matter of fact, Cabell took the thing to heart. He
used to know Miss Lipscomb in Virginia—she comes from another famous family
there—and he seemed to think he had a prior claim on her.”

Hatch heard
all these things as any man might listen to gossip, but each additional fact
was sinking into his mind, and each additional fact led his suspicions on
deeper into the channel they had chosen.

“Cabell is
pretty well to do,” his informant went on, “not rich as we count riches in the
North, but pretty well to do, and I believe he came to Boston because Miss
Lipscomb spent so much of her time here. She is a beautiful young woman of
twenty-two and extremely popular in the social world everywhere, particularly
in Boston. Then there was the additional fact that Henley was here.”

“No chance at
all for Cabell?” Hatch suggested.

“Not the
slightest,” was the reply. “Yet despite the heartbreak he had, he was the first
to congratulate Henley on winning her love. And he meant it, too.”

“What’s his
attitude toward Henley now?” asked Hatch. His voice was calm, but there was an
underlying tense note imperceptible to the other.

“They meet and
speak and move in the same set. There’s no love lost on either side, I don’t
suppose, but there is no trace of any ill feeling.”

“Cabell
doesn’t happen to be a vindictive sort of man?”

“Vindictive?”
and the other laughed. “No. He’s like a big boy, forgiving, and all that;
hot-tempered, though. I could imagine him in a fit of anger making a personal
matter of it with Henley, but I don’t think he ever did.”

The mind of
the newspaper man was rapidly focusing on one point; the rush of thoughts, questions
and doubts silenced him for a moment. Then:

“How long has
Cabell been in Boston?”

“Seven or
eight months—that is, he has had apartments here for that long—but he has made
several visits South. I suppose it’s South. He has a trick of dropping out of
sight occasionally. I understand that he intends to go South for good very
soon. If I’m not mistaken, he is trying now to rent his suite.”

Hatch looked
suddenly at his informant; an idea of seeing Cabell and having a legitimate
excuse for talking to him had occurred to him.

“I’m looking
for a suite,” he volunteered at last. “I wonder if you would give me a card of
introduction to him? We might get together on it.”

Thus it
happened that half an hour later, about ten minutes past nine o’clock, Hatch
was on his way to the big apartment house. In the office he saw the manager.

“Heard the
news?” asked the manager.

“No,” Hatch
replied. “What is it?”

“Somebody’s
shot Mr. Henley as he was passing through the Common early to-night.”

Hatch whistled
in amazement.

“Is he dead?”

“No, but he is
unconscious. The hospital doctors say it is a nasty wound, but not necessarily
dangerous.”

“Who shot him?
Do they know?”

“He knows, but
he won’t say.”

Amazed and
alarmed by this latest development, an accurate fulfillment of The Thinking
Machine’s prophecy, Hatch stood thoughtful for a moment, then recovering his
composure a little asked for Cabell.

“I don’t think
there’s much chance of seeing him,” said the manager. “He’s going away on the
midnight train—going South, to Virginia.”

“Going away
to-night?” Hatch gasped.

“Yes; it seems
to have been rather a sudden determination. He was talking to me here half an
hour or so ago, and said something about going away. While he was here the
telephone boy told me that Henley had been shot; they had ’phoned from the
hospital to inform us. Then Cabell seemed greatly agitated. He said he was
going away to-night, if he could catch the midnight train, and now he’s
packing.”

“I suppose the
shooting of Henley upset him considerably?” the reporter suggested.

“Yes, I guess
it did,” was the reply. “They moved in the same set and belonged to the same
clubs.”

The manager
sent Hatch’s card of introduction to Cabell’s apartments. Hatch went up and was
ushered into a suite identical with that of Henley’s in every respect save in
minor details of furnishings. Cabell stood in the middle of the floor, with his
personal belongings scattered about the room; his valet, evidently a Frenchman,
was busily engaged in packing.

Cabell’s
greeting was perfunctorily cordial; he seemed agitated. His face was flushed
and from time to time he ran his fingers through his long, brown hair. He
stared at Hatch in a preoccupied fashion, then they fell into conversation
about the rent of the apartments.

“I’ll take
almost anything reasonable,” Cabell said hurriedly. “You see, I am going away
to-night, rather more suddenly than I had intended, and I am anxious to get the
lease off my hands. I pay two hundred dollars a month for these just as they
are.”

“May I looked
them over?” asked Hatch.

He passed from
the front room into the next. Here, on a bed, was piled a huge lot of clothing,
and the valet, with deft fingers, was brushing and folding, preparatory to
packing. Cabell was directly behind him.

“Quite
comfortable, you see,” he explained. “There’s room enough if you are alone. Are
you?”

“Oh, yes,”
Hatch replied.

“This other
room here,” Cabell explained, “is not in very tidy shape now. I have been out
of the city for several weeks, and—— What’s the matter?” he demanded suddenly.

Hatch had
turned quickly at the words and stared at him, then recovered himself with a
start.

“I beg your
pardon,” he stammered. “I rather thought I saw you in town here a week or so
ago—of course I didn’t know you—and I was wondering if I could have been
mistaken.”

“Must have
been,” said the other easily. “During the time I was away a Miss ——, a friend
of my sister’s, occupied the suite. I’m afraid some of her things are here. She
hasn’t sent for them as yet. She occupied this room, I think; when I came back
a few days ago she took another place and all her things haven’t been removed.”

“I see,”
remarked Hatch, casually. “I don’t suppose there’s any chance of her returning
here unexpectedly if I should happen to take her apartments?”

“Not the
slightest. She knows I am back, and thinks I am to remain. She was to send for
these things.”

Hatch gazed
about the room ostentatiously. Across a trunk lay a Turkish bath robe with a
scarlet stripe in it. He was anxious to get hold of it, to examine it closely.
But he didn’t dare to, then. Together they returned to the front room.

“I rather like
the place,” he said, after a pause, “but the price is——”

“Just a
moment,” Cabell interrupted. “Jean, before you finish packing that suit case be
sure to put my bath robe in it. It’s in the far room.”

Then one
question was settled for Hatch. After a moment the valet returned with the bath
robe, which had been in the far room. It was Cabell’s bath robe. As Jean passed
the reporter an end of the robe caught on a corner of the trunk, and, stopping,
the reporter unfastened it. A tiny strand of thread clung to the metal; Hatch
detached it and stood idly twirling it in his fingers.

“As I was
saying,” he resumed, “I rather like the place, but the price is too much. Suppose
you leave it in the hands of the manager of the house——”

“I had
intended doing that,” the Southerner interrupted.

“Well, I’ll
see him about it later,” Hatch added.

With a
cordial, albeit pre-occupied, handshake, Cabell ushered him out. Hatch went down
in the elevator with a feeling of elation; a feeling that he had accomplished
something. The manager was waiting to get into the lift.

“Do you happen
to remember the name of the young lady who occupied Mr. Cabell’s suite while he
was away?” he asked.

“Miss Austin,”
said the manager, “but she’s not young. She was about forty-five years old, I
should judge.”

“Did Mr.
Cabell have his servant Jean with him?”

“Oh, no,” said
the manager. “The valet gave up the suite to Miss Austin entirely, and until
Mr. Cabell returned occupied a room in the quarters we have for our own
employees.”

“Was Miss
Austin ailing in any way?” asked Hatch. “I saw a large number of medicine
bottles upstairs.”

“I don’t know
what was the matter with her,” replied the manager, with a little puzzled
frown. “She certainly was not a woman of sound mental balance—that is, she was
eccentric, and all that. I think rather it was an act of charity for Mr. Cabell
to let her have the suite in his absence. Certainly we didn’t want her.”

Hatch passed
out and burst in eagerly upon The Thinking Machine in his laboratory.

“Here,” he
said, and triumphantly he extended the tiny scarlet strand which he had
received from The Thinking Machine, and the other of the identical color which
came from Cabell’s bath robe. “Is that the same?”

The Thinking
Machine placed them under the microscope and examined them immediately. Later
he submitted them to a chemical test.

“It is the same,” he said, finally.

“Then the
mystery is solved,” said Hatch, conclusively.

V

The Thinking
Machine stared steadily into the
eager, exultant eyes of the newspaper man until Hatch at last began to fear
that he had been precipitate. After awhile, under close scrutiny, the reporter
began to feel convinced that he had made a mistake—he didn’t quite see where,
but it must be there, and the exultant manner passed. The voice of The Thinking
Machine was like a cold shower.

“Remember, Mr.
Hatch,” he said, critically, “that unless every possible question has been
considered one cannot boast of a solution. Is there any possible question
lingering yet in your mind?”

The reporter
silently considered that for a moment, then:

“Well, I have
the main facts, anyway. There may be one or two minor questions left, but the
principal ones are answered.”

“Then tell me,
to the minutest detail, what you have learned, what has happened.”

Professor Van
Dusen sank back in his old, familiar pose in the large arm chair and Hatch
related what he had learned and what he surmised. He related, too, the peculiar
circumstances surrounding the wounding of Henley, and right on down to the
beginning and end of the interview with Cabell in the latter’s apartments. The
Thinking Machine was silent for a time, then there came a host of questions.

“Do you know
where the woman—Miss Austin—is now?” was the first.

“No,” Hatch
had to admit.

“Or her
precise mental condition?”

“No.”

“Or her exact
relationship to Cabell?”

“No.”

“Do you know,
then, what the valet, Jean, knows of the affair?”

“No, not
that,” said the reporter, and his face flushed under the close questioning. “He
was out of the suite every night.”

“Therefore
might have been the very one who turned on the gas,” the other put in testily.

“So far as I
can learn, nobody could have gone into that room and turned on the gas,” said
the reporter, somewhat aggressively. “Henley barred the doors and windows and
kept watch, night after night.”

“Yet the
moment he was exhausted and fell asleep the gas was turned on to kill him,”
said The Thinking Machine; “thus we see that he was watched more closely than he watched.”

“I see what
you mean now,” said Hatch, after a long pause.

“I should like
to know what Henley and Cabell and the valet knew of the girl who was found
dead,” The Thinking Machine suggested. “Further, I should like to know if there
was a good-sized mirror—not one set in a bureau or dresser—either in Henley’s
room or the apartments where the girl was found. Find out this for me and—never
mind. I’ll go with you.”

The scientist
left the room. When he returned he wore his coat and hat. Hatch arose
mechanically to follow. For a block or more they walked along, neither
speaking. The Thinking Machine was the first to break the silence:

“You believe
Cabell is the man who attempted to kill Henley?”

“Frankly, yes,”
replied the newspaper man.

“Why?”

“Because he
had the motive—disappointed love.”

“How?”

“I don’t
know,” Hatch confessed. “The doors of the Henley suite were closed. I don’t see
how anybody passed them.”

“And the girl?
Who killed her? How? Why?”

Disconsolately
Hatch shook his head as he walked on. The Thinking Machine interpreted his
silence aright.

“Don’t jump at
conclusions,” he advised sharply. “You were confident Cabell was to blame for
this—and he might have been, I don’t know yet—but you can suggest nothing to
show how he did it. I have told you before that imagination is half of logic.”

At last the
lights of the big apartment house where Henley lived came in sight. Hatch
shrugged his shoulders. He had grave doubts—based on what he knew—whether The
Thinking Machine would be able to see Cabell. It was nearly eleven o’clock and
Cabell was to leave for the South at midnight.

“Is Mr. Cabell
here?” asked the scientist of the elevator boy.

“Yes, just
about to go, though. He won’t see anyone.”

“Hand him this
note,” instructed The Thinking Machine, and he scribbled something on a piece
of paper. “He’ll see us.”

The boy took
the paper and the elevator shot up to the fourth floor. After awhile he
returned.

“He’ll see
you,” he said.

“Is he unpacking?”

“After he read
your note twice he told his valet to unpack,” the boy replied.

“Ah, I thought
so,” said The Thinking Machine.

With Hatch,
mystified and puzzled, following, The Thinking Machine entered the elevator to
step out a second or so later on the fourth floor. As they left the car they
saw the door of Cabell’s apartment standing open; Cabell was in the door. Hatch
traced a glimmer of anxiety in the eyes of the young man.

“Professor Van
Dusen?” Cabell inquired.

“Yes,” said
the scientist. “It was of the utmost importance that I should see you,
otherwise I should not have come at this time of night.”

With a wave of
his hand Cabell passed that detail.

“I was anxious
to get away at midnight,” he explained, “but, of course, now I shan’t go, in view
of your note. I have ordered my valet to unpack my things, at least until
to-morrow.”

The reporter
and the scientist passed into the luxuriously furnished apartments. Jean, the
valet, was bending over a suit case as they entered, removing some things he
had been carefully placing there. He didn’t look back or pay the least
attention to the visitors.

“This is your
valet?” asked The Thinking Machine.

“Yes,” said
the young man.

“French, isn’t
he?”

“Yes.”

“Speak English
at all?”

“Very badly,”
said Cabell. “I use French when I talk to him.”

“Does he know
that you are accused of murder?” asked The Thinking Machine, in a quiet,
conversational tone.

The effect of
the remark on Cabell was startling. He staggered back a step or so as if he had
been struck in the face, and a crimson flush overspread his brow. Jean, the
valet, straightened up suddenly and looked around. There was a queer
expression, too, in his eyes; an expression which Hatch could not fathom.

“Murder?”
gasped Cabell, at last.

“Yes, he speaks
English all right,” remarked The Thinking Machine. “Now, Mr. Cabell, will you
please tell me just who Miss Austin is, and where she is, and her mental
condition? Believe me, it may save you a great deal of trouble. What I said in
the note is not exaggerated.”

The young man
turned suddenly and began to pace back and forth across the room. After a few
minutes he paused before The Thinking Machine, who stood impatiently waiting
for an answer.

“I’ll tell
you, yes,” said Cabell, firmly. “Miss Austin is a middle-aged woman whom my
sister befriended several times—was, in fact, my sister’s governess when she
was a child. Of late years she has not been wholly right mentally, and has
suffered a great deal of privation. I had about concluded arrangements to put her
in a private sanitarium. I permitted her to remain in these rooms in my
absence, South. I did not take Jean—he lived in the quarters of the other
employees of the place, and gave the apartment entirely to Miss Austin. It was
simply an act of charity.”

“What was the
cause of your sudden determination to go South to-night?” asked the scientist.

“I won’t
answer that question,” was the sullen reply.

There was a
long, tense silence. Jean, the valet, came and went several times.

“How long has
Miss Austin known Mr. Henley?”

“Presumably
since she has been in these apartments,” was the reply.

“Are you sure you are not Miss Austin?” demanded the
scientist.

The question
was almost staggering, not only to Cabell, but to Hatch. Suddenly, with flaming
face, the young Southerner leaped forward as if to strike down The Thinking
Machine.

“That won’t do
any good,” said the scientist, coldly. “Are you sure you are not Miss Austin?”
he repeated.

“Certainly I
am not Miss Austin,” responded Cabell, fiercely.

“Have you a
mirror in these apartments about twelve inches by twelve inches?” asked The
Thinking Machine, irrelevantly.

“I—I don’t
know,” stammered the young man. “I—have we, Jean?”

“Oui,” replied the valet.

“Yes,” snapped
The Thinking Machine. “Talk English, please. May I see it?”

The valet,
without a word but with a sullen glance at the questioner, turned and left the
room. He returned after a moment with the mirror. The Thinking Machine
carefully examined the frame, top and bottom and on both sides. At last he
looked up; again the valet was bending over a suit case.

“Do you use
gas in these apartments?” the scientist asked suddenly.

“No,” was the
bewildered response. “What is all this, anyway?”

Without
answering, The Thinking Machine drew a chair up under the chandelier where the
gas and electric fixtures were and began to finger the gas tips. After awhile
he climbed down and passed into the next room, with Hatch and Cabell, both
hopelessly mystified, following. There the scientist went through the same process
of fingering the gas jets. Finally, one of the gas tips came out in his hand.

“Ah,” he
exclaimed, suddenly, and Hatch knew the note of triumph in it. The jet from
which the tip came was just on a level with his shoulder, set between a
dressing table and a window. He leaned over and squinted at the gas pipe
closely. Then he returned to the room where the valet was.

“Now, Jean,”
he began, in an even, calm voice, “please tell me if you did or did not kill Miss Regnier purposely?”

“I don’t know
what you mean,” said the servant sullenly, angrily, as he turned on the
scientist.

“You speak
very good English now,” was The Thinking Machine’s terse comment. “Mr. Hatch,
lock the door and use this ’phone to call the police.”

Hatch turned
to do as he was bid and saw a flash of steel in young Cabell’s hand, which was
drawn suddenly from a hip pocket. It was a revolver. The weapon glittered in
the light, and Hatch flung himself forward. There was a sharp report, and a
bullet was buried in the floor.

VI

Then came a fierce, hard fight for
possession of the revolver. It ended with the weapon in Hatch’s hand, and both
he and Cabell blowing from the effort they had expended. Jean, the valet, had
turned at the sound of the shot and started toward the door leading into the
hall. The Thinking Machine had stepped in front of him, and now stood there
with his back to the door. Physically he would have been a child in the hands
of the valet, yet there was a look in his eyes which stopped him.

“Now, Mr.
Hatch,” said the scientist quietly, a touch of irony in his voice, “hand me the
revolver, then ’phone for Detective Mallory to come here immediately. Tell him
we have a murderer—and if he can’t come at once get some other detective whom
you know.”

“Murderer!”
gasped Cabell.

Uncontrollable
rage was blazing in the eyes of the valet, and he made as if to throw The
Thinking Machine aside, despite the revolver, when Hatch was at the telephone.
As Jean started forward, however, Cabell stopped him with a quick, stern
gesture. Suddenly the young Southerner turned on The Thinking Machine; but it
was with a question.

“What does it
all mean?” he asked, bewildered.

“It means that
that man there,” and The Thinking Machine indicated the valet by a nod of his
head, “is a murderer—that he killed Louise Regnier; that he shot Welden Henley
on Boston Common, and that, with the aid of Miss Regnier, he had four times
previously attempted to kill Mr. Henley. Is he coming, Mr. Hatch?”

“Yes,” was the
reply. “He says he’ll be here directly.”

“Do you deny
it?” demanded The Thinking Machine of the valet.

“I’ve done
nothing,” said the valet sullenly. “I’m going out of here.”

Like an
infuriated animal he rushed forward. Hatch and Cabell seized him and bore him
to the floor. There, after a frantic struggle, he was bound and the other three
men sat down to wait for Detective Mallory. Cabell sank back in his chair with
a perplexed frown on his face. From time to time he glanced at Jean. The flush
of anger which had been on the valet’s face was gone now; instead there was the
pallor of fear.

“Won’t you
tell us?” pleaded Cabell impatiently.

“When
Detective Mallory comes and takes his prisoner,” said The Thinking Machine.

Ten minutes
later they heard a quick step in the hall outside and Hatch opened the door.
Detective Mallory entered and looked from one to another inquiringly.

“That’s your
prisoner, Mr. Mallory,” said the scientist, coldly. “I charge him with the
murder of Miss Regnier, whom you were so confident committed suicide; I charge
him with five attempts on the life of Weldon Henley, four times by gas
poisoning, in which Miss Regnier was his accomplice, and once by shooting. He
is the man who shot Mr. Henley.”

The Thinking
Machine arose and walked over to the prostate man, handing the revolver to
Hatch. He glared down at Jean fiercely.

“Will you tell
how you did it or shall I?” he demanded.

His answer was
a sullen, defiant glare. He turned and picked up the square mirror which the
valet had produced previously.

“That’s where
the screw was, isn’t it?” he asked, as he indicated a small hole in the frame
of the mirror. Jean stared at it and his head sank forward hopelessly. “And
this is the bath robe you wore, isn’t it?” he demanded again, and from the suit
case he pulled out the garment with the scarlet stripe.

“I guess you
got me all right,” was the sullen reply.

“It might be
better for you if you told the story then?” suggested The Thinking Machine.

“You know so
much about it, tell it yourself.”

“Very well,”
was the calm rejoinder. “I will. If I make any mistake you will correct me.”

For a long
time no one spoke. The Thinking Machine had dropped back into a chair and was
staring through his thick glasses at the ceiling; his finger tips were pressed
tightly together. At last he began:

“There are
certain trivial gaps which only the imagination can supply until the matter is
gone into more fully. I should have supplied these myself, but the arrest of
this man, Jean, was precipitated by the attempted hurried departure of Mr.
Cabell for the South to-night, and I did not have time to go into the case to
the fullest extent.

“Thus, we
begin with the fact that there were several clever attempts made to murder Mr.
Henley. This was by putting out the gas which he habitually left burning in his
room. It happened four times in all; thus proving that it was an attempt to
kill him. If it had been only once it might have been accident, even twice it
might have been accident, but the same accident does not happen four times at
the same time of night.

“Mr. Henley
finally grew to regard the strange extinguishing of the gas as an effort to
kill him, and carefully locked and barred his door and windows each night. He
believed that some one came into his apartments and put out the light, leaving
the gas flow. This, of course, was not true. Yet the gas was put out. How? My
first idea, a natural one, was that it was turned off for an instant at the
meter, when the light would go out, then turned on again. This, I convinced
myself, was not true. Therefore still the question—how?

“It is a
fact—I don’t know how widely known it is—but it is a fact that every gas light
in this house might be extinguished at the same time from this room without
leaving it. How? Simply by removing that gas jet tip and blowing into the gas
pipe. It would not leave a jet in the building burning. It is due to the fact
that the lung power is greater than the pressure of the gas in the pipes, and
forces it out.

“Thus we have
the method employed to extinguish the light in Mr. Henley’s rooms, and all the
barred and locked doors and windows would not stop it. At the same time it
threatened the life of every other person in the house—that is, every other person
who used gas. It was probably for this reason that the attempt was always made
late at night, I should say three or four o’clock. That’s when it was done,
isn’t it?” he asked suddenly of the valet.

Staring at The
Thinking Machine in open-mouthed astonishment the valet nodded his acquiescence
before he was fully aware of it.

“Yes, that’s
right,” The Thinking Machine resumed complacently. “This was easily found
out—comparatively. The next question was how was a watch kept on Mr. Henley? It
would have done no good to extinguish the gas before he was asleep, or to have
turned it on when he was not in his rooms. It might have led to a speedy
discovery of just how the thing was done.

“There’s a
spring lock on the door of Mr. Henley’s apartment. Therefore it would have been
impossible for anyone to peep through the keyhole. There are no cracks through
which one might see. How was this watch kept? How was the plotter to satisfy
himself positively of the time when Mr. Henley was asleep? How was it that the
gas was put out at no time of the score or more nights Mr. Henley himself kept
watch? Obviously he was watched through a window.

“No one could
climb out on the window ledge and look into Mr. Henley’s apartments. No one
could see into that apartment from the street—that is, could see whether Mr.
Henley was asleep or even in bed. They could see the light. Watch was kept with
the aid offered by the flagpole, supplemented with a mirror—this mirror. A
screw was driven into the frame—it has been removed now—it was swung on the
flagpole rope and pulled out to the end of the pole, facing the building. To a
man standing in the hall window of the third floor it offered precisely the
angle necessary to reflect the interior of Mr. Henley’s suite, possibly even
showed him in bed through a narrow opening in the curtain. There is no shade on
the windows of that suite; heavy curtains instead. Is that right?”

Again the prisoner
was surprised into a mute acquiescence.

“I saw the
possibility of these things, and I saw, too, that at three or four o’clock in
the morning it would be perfectly possible for a person to move about the upper
halls of this house without being seen. If he wore a heavy bath robe, with a
hood, say, no one would recognize him even if he were seen, and besides the
garb would not cause suspicion. This bath robe has a hood.

“Now, in
working the mirror back and forth on the flagpole at night a tiny scarlet
thread was pulled out of the robe and clung to the rope. I found this thread;
later Mr. Hatch found an identical thread in these apartments. Both came from
that bath robe. Plain logic shows that the person who blew down the gas pipes
worked the mirror trick; the person who worked the mirror trick left the
thread; the thread comes back to the bath robe—that bath robe there,” he
pointed dramatically. “Thus the person who desired Henley’s death was in these
apartments, or had easy access to them.”

He paused for
a moment and there was a tense silence. A great light was coming to Hatch,
slowly but surely. The brain that had followed all this was unlimited in
possibilities.

“Even before
we traced the origin of the crime to this room,” went on the scientist, quietly
now, “attention had been attracted here, particularly to you, Mr. Cabell. It
was through the love affair, of which Miss Lipscomb was the center. Mr. Hatch
learned that you and Henley had been rivals for her hand. It was that, even
before this scarlet thread was found, which indicated that you might have some
knowledge of the affair, directly or indirectly.

“You are not a
malicious or revengeful man, Mr. Cabell. But you are hot-tempered—extremely so.
You demonstrated that just now, when, angry and not understanding, but feeling
that your honor was at stake, you shot a hole in the floor.”

“What?” asked
Detective Mallory.

“A little
accident,” explained The Thinking Machine quickly. “Not being a malicious or
revengeful man, you are not the man to deliberately go ahead and make elaborate
plans for the murder of Henley. In a moment of passion you might have killed
him—but never deliberately as the result of premeditation. Besides you were out
of town. Who was then in these apartments? Who had access to these apartments?
Who might have used your bath robe? Your valet, possibly Miss Austin. Which?
Now, let’s see how we reached this conclusion which led to the valet.

“Miss Regnier
was found dead. It was not suicide. How did I know? Because she had been reading
with the gas light at its full. If she had been reading by the gas light, how
was it then that it went out and suffocated her before she could arise and shut
it off? Obviously she must have fallen asleep over her book and left the light
burning.

“If she was in
this plot to kill Henley, why did she light the jet in her room? There might
have been some defect in the electric bulb in her room which she had just
discovered. Therefore she lighted the gas, intending to extinguish it—turn it
off entirely—later. But she fell asleep. Therefore when the valet here blew
into the pipe, intending to kill Mr. Henley, he unwittingly killed the woman he
loved—Miss Regnier. It was perfectly possible, meanwhile, that she did not know
of the attempt to be made that particular night, although she had participated
in the others, knowing that Henley had night after night sat up to watch the
light in his rooms.

“The facts, as
I knew them, showed no connection between Miss Regnier and this man at that
time—nor any connection between Miss Regnier and Henley. It might have been
that the person who blew the gas out of the pipe from these rooms knew nothing
whatever of Miss Regnier, just as he didn’t know who else he might have killed
in the building.

“But I had her
death and the manner of it. I had eliminated you, Mr. Cabell. Therefore there
remained Miss Austin and the valet. Miss Austin was eccentric—insane, if you
will. Would she have any motive for killing Henley? I could imagine none. Love?
Probably not. Money? They had nothing in common on that ground. What? Nothing
that I could see. Therefore, for the moment, I passed Miss Austin by, after
asking you, Mr. Cabell, if you were Miss Austin.

“What
remained? The valet. Motive? Several possible ones, one or two probable. He is
French, or says he is. Miss Regnier is French. Therefore I had arrived at the
conclusion that they knew each other as people of the same nationality will in
a house of this sort. And remember, I had passed by Mr. Cabell and Miss Austin,
so the valet was the only one left; he could use the bath robe.

“Well, the
motive. Frankly that was the only difficult point in the entire
problem—difficult because there were so many possibilities. And each
possibility that suggested itself suggested also a woman. Jealousy? There must
be a woman. Hate? Probably a woman. Attempted extortion? With the aid of a
woman. No other motive which would lead to so elaborate a plot of murder would
come forward. Who was the woman? Miss Regnier.

“Did Miss
Regnier know Henley? Mr. Hatch had reason to believe he knew her because of his
actions when informed of her death. Knew her how? People of such relatively
different planes of life can know each other—or do know each other—only on one
plane. Henley is a typical young man, fast, I dare say, and liberal. Perhaps,
then, there had been a liason. When I saw this possibility I had my motives—all
of them—jealousy, hate and possibly attempted extortion as well.

“What was more
possible than Mr. Henley and Miss Regnier had been acquainted? All liasons are
secret ones. Suppose she had been cast off because of the engagement to a young
woman of Henley’s own level? Suppose she had confided in the valet here? Do you
see? Motives enough for any crime, however diabolical. The attempts on Henley’s
life possibly followed an attempted extortion of money. The shot which wounded
Henley was fired by this man, Jean. Why? Because the woman who had cause to
hate Henley was dead. Then the man? He was alive and vindictive. Henley knew
who shot him, and knew why, but he’ll never say it publicly. He can’t afford
to. It would ruin him. I think probably that’s all. Do you want to add
anything?” he asked the valet.

“No,” was the
fierce reply. “I’m sorry I didn’t kill him, that’s all. It was all about as you
said, though God knows how you found it out,” he added, desperately.

“Are you a
Frenchman?”

“I was born in
New York, but lived in France for eleven years. I first knew Louise there.”

Silence fell
upon the little group. Then Hatch asked a question:

“You told me,
Professor, that there would be no other attempt to kill Henley by extinguishing
the gas. How did you know that?”

“Because one
person—the wrong person—had been killed that way,” was the reply. “For this
reason it was hardly likely that another attempt of that sort would be made.
You had no intention of killing Louise Regnier, had you, Jean?”

“No, God help
me, no.”

“It was all
done in these apartments,” The Thinking Machine added, turning to Cabell, “at
the gas jet from which I took the tip. It had been only loosely replaced and
the metal was tarnished where the lips had dampened it.”

“It must take
great lung power to do a thing like that,” remarked Detective Mallory.

“You would be
amazed to know how easily it is done,” said the scientist. “Try it some time.”

The Thinking
Machine arose and picked up his hat; Hatch did the same. Then the reporter
turned to Cabell.

“Would you
mind telling me why you were so anxious to get away to-night?” he asked.

“Well, no,”
Cabell explained, and there was a rush of red to his face. “It’s because I
received a telegram from Virginia—Miss Lipscomb, in fact. Some of Henley’s past
had come to her knowledge and the telegram told me that the engagement was
broken. On top of this came the information that Henley had been shot and—I was
considerably agitated.”

The Thinking
Machine and Hatch were walking along the street.

“What did you
write in the note you sent to Cabell that made him start to unpack?” asked the
reporter, curiously.

“There are
some things that it wouldn’t be well for everyone to know,” was the enigmatic
response. “Perhaps it would be just as well for you to overlook this little
omission.”